(a) Field of the Invention
The present invention relates to liquid crystal displays (LCDs) and a manufacturing method thereof, in particular, to structures of liquid crystal displays having pixel electrodes and common electrodes in a substrate and a manufacturing method thereof.
(b) Description of the Related Art
Generally, liquid crystal displays (LCDs) include two substrates facing each other and a liquid crystal layer injected between the substrates. Images of the LCD are displayed by controlling the light transmittance of the liquid crystal layer.
In an LCD mode having pixel electrodes and common electrodes in one substrate, an electric field is generated parallel to the surfaces of the substrates so that long axes of liquid crystal molecules are operated in parallel to the surfaces of the substrates. Therefore, a viewing angle becomes enhanced.
An LCD according to the conventional invention now will be described with reference to the accompanying drawings.
FIG. 1 is a layout view of an LCD according to the conventional invention. FIG. 2 is a cross sectional view of a thin film transistor taken along line II-IIxe2x80x2 in FIG. 1, and FIG. 3 is a cross sectional view taken along line III-IIIxe2x80x2 in FIG. 1.
As shown in FIG. 1 to FIG. 3, gate lines 200 are formed on a substrate 100 and arranged in the horizontal direction. The first common electrode line 301 and the second common electrode lines 302 are formed parallel to the gate lines 200. A plurality of common electrodes 310 are arranged in the vertical direction in FIG. 1, extend from the first common electrode line 301 and connect to the second common electrode line 302.
A gate insulating film 400 covers the gate line 200, the first and the second electrode lines 301 and 302, and the common electrodes 310. An amorphous silicon layer 500 is formed on the gate insulating film 400 and overlaps a portion of the gate line 200 playing a role as the gate electrode. Data lines 700 are formed on the gate insulating film 400 and arranged in the vertical direction in FIG. 1. A source electrode 710 is extended from the date line 700 and partially overlaps the amorphous silicon layer 500, and a drain electrode 720 is formed opposite the source electrode 710 and partially overlaps the amorphous silicon layer 500. Doped amorphous silicon layers 610 and 620 are formed between the amorphous silicon layer 500 and the source 710 and the drain electrodes 720 to improve contact characteristics.
A pixel electrode line 800 is extended from the drain electrode 720 and overlaps the first common electrode line 301. A plurality of pixel electrodes 810 is extended from the pixel electrode line 800 and arranged parallel to the data line 700 and the common electrodes 310. Each the pixel electrode 810 is located between the two common electrodes 310.
As described above, since the pixel electrode 810 and the common electrodes 310 are formed in the same substrate 100 and parallel to each other, an generated electric field is substantially parallel to the surface of the substrate 100.
The electric field and an arrangement of the liquid crystal in the LCD according to the conventional invention now will be described hereinafter.
FIG. 4 is a cross sectional view showing the electric field and the arrangement of the liquid crystal molecules.
As shown in FIG. 4, a common electrode 310 is formed on the first substrate 100 for a thin film transistor substrate and arranged parallel to a pixel electrode 810 and a data line 700 via a gate insulating film 400. The second substrate 110 having a light-blocking film 120 corresponds to face the first substrate 100 and a liquid crystal layer (LC) is interposed therebetween. The light-blocking film 120 is located between two pixels, and arranged to face the data line 700 and a portion of the common electrode 310 adjoining the data line 700
The liquid crystal layer (LC) of the above-described LCD is operated by a potential difference between the common electrode 310 and the pixel electrode 810. In more detail, either a direct-current (DC) voltage or an alternating-current (AC) is applied to the common electrode 310. Display signals are applied to the pixel electrode 810 through the data line 700 when the thin film transistor (TFT) is in the on-state. If the TFT gets turned off, the signals applied to the pixel electrode 810 are stored until the TFT gets turned on again.
As illustrated in FIG. 4, electric field lines E perpendicular to equipotential lines Peq are substantially parallel to the surface of the substrates 100 and 110 between the electrodes 310 and 810. However, an abnormal arrangement of the liquid crystal molecules occurs between the common electrode 310 adjoining to the data line 700 and the pixel electrode 810. This phenomenon of an unwanted abnormal arrangement is defined as a disclination. One cause of the disclination is the electric voltage differences between the voltages applied and stored to the pixel electrode 810 and voltages applied to the data line 700. As the electric voltage difference between the data line 700 and the pixel electrode 810 is increased and the distance between the data line 700 and the pixel electrode 810 is narrowed, the disclination region of the liquid crystal layer LC becomes wider. A signal variation of the data line 700 is another cause of the disclination. That is, since the adjoining common electrode 310 is affected by the signal variation, the status of the electric field is changed.
In the disclination region, light-leakage may occur. That is, light tansmitted by the disclination region is partially blocked by the blocking film 120 overlapping the data line 700 and a part of the adjoining common electrode 310. However, as shown in FIG. 4, if the disclination region is wide, the light-leakage still occurs through a region A which is not blocked by the blocking film 120.
Additionally, even when light passing through the disclination region is initially blocked by the light-blocking film 120, it is possible that light-leakage still occurs around the light-blocking film 120. This is because reflection of light occurs at the surface of the blocking film 120 which is made of metals such as Cr and then reflects again off of the common electrode 310 or the pixel electrode 810.
Since this light-leakage phenomenon occurs at pixels along the data lines 700, a vertical cross-talk effect by which a white line is generated in a normally black state display screen occurs.
One method to prevent the vertical cross-talk is overlapping a common electrode and the adjoining data line. However, since a parasitic capacitance occurs near the overlapping portion of the data line and the common electrode, the driving IC may be abnormally heated while being operated. Another method to prevent the cross-talk is forming the light-blocking film from an organic film. However, as this would require a different method of recognizing alignment keys, extra equipment investment will be needed.
The present invention has been made in an effort to solve the above problems.
It is an object of the present invention to reduce the disclination region of liquid crystal layer to decrease cross-talk.
It is another object of the present invention to prevent the cross-talk without generation of heat in driving circuits or an increase of the manufacturing cost due to an equipment investment.
To achieve the above objects, a liquid crystal display according to an embodiment of the present invention provides a field-blocking film which overlaps edges of a data line via an insulating film and blocks an electric field generated from the data line.
The field-blocking webbing may be made by partially overlapping a common electrode adjoining to the data line and connect to the common electrode.
Gate lines may be formed on the same layer as the data line. The gate line is divided into a plurality of portions, which are separated from the data lines. The portions are connected to each other by connect patterns formed on an insulating film covering the gate lines and the data lines. Moreover, the common electrodes may be formed on the same layer as the data line. In this case, the common electrodes of two adjacent pixels connect to each other by the electric field blocking webbing which is formed on the insulating film and overlaps the data line and the common electrode.
In this embodiment, switching devices may be included. The switching devices play a role of transmitting image signals from the data lines to the pixel electrodes according to scan signals from the gate lines.
To achieve above objects, in a liquid crystal display according to another embodiment of the present invention, data lines are located on a lower layer than common electrodes and do not overlap the common electrodes. In other words, data lines are formed on a lower substrate in one direction and a gate insulating film covers the data lines. On the gate insulating film, gate lines are formed perpendicular to the data lines, common electrode lines are formed parallel to the gate lines, and a plurality of common electrodes are extended from the common electrode line. The common electrodes are arranged parallel to the data lines. A light-blocking film is formed on one surface of an upper substrate facing the lower substrate. The light-blocking film overlaps the data line and a part of the common electrode adjoining to the data line.
It is required that the common electrode adjoining the data line does not overlap the data line.
Secondary data lines may be formed on an interlayer insulating film covering the common electrodes and electrically connect to the data lines. The secondary data lines are required not to overlap the common electrodes.
In the case that the data line is formed below the common electrode, since directions of light transmitting through the gap between the data line and the common electrode are different from in the conventional structure, the light is mostly blocked by the light-blocking film. In addition, since an incident angle of the light is large, the intensity of the light is decreased while being reflected several times on the light-blocking film and the common electrodes.